chore: test if downgrades trigger enforcer errors.

Author: blakeli0

java-spanner/google-cloud-spanner/pom.xml

@@ -191,6 +191,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>grpc-gcp</artifactId>
+      <version>1.9.0</version>
       <exclusions>
          <exclusion>
             <groupId>io.opentelemetry</groupId>